The paper describes a simple empirical model of
bitstreams produced by MPEG-2 video coders. The
number of bits that represent an I- or P-frame is expressed
as a function of the quantization factor Q. This model is
global in the sense that it describes the total number of
bits in a frame thus ignoring local bitrate variation within
a frame as well as changes of Q within a frame. This fiveparameter
model fits well to experimental data. Four of
these parameters may be fixed thus obtaining less accurate
one-parameter model that can be used for coder control.
The experimental results are reported for some video test
sequences in the BT.601/4CIF format encoded by an
MPEG-2 MP@ML coder.